Roll-up doors may be used in a variety of environments. Such roll-up doors typically include a curtain which may be wound or unwound from a horizontally disposed roller, typically in place above the doorway which is to be blocked and unblocked by the curtain. The door is closed by rotating the roller such that the curtain pays off of the roller to block the doorway. The door is then opened by rolling the roller in an opposite direction. One example of a roll-up door is a door that is actuated like a window shade -- with manual actuation down and a spring-loaded roller for causing the door to roll-up when properly released. Such manual roll-down, spring-loaded roll-up doors are typically used in a light-duty environment. For example, such a door may be used in combination with a heavy-duty door in the exterior doorway of a loading dock in a manufacturing or warehouse facility. In such an installation, the heavy-duty door is typically used to prevent or allow authorized access to the doorway. Typical doors used for this purpose are manual or powered roll-up doors or so-called overhead doors (e.g. a garage-type sectioned door moveable from a vertical blocking position, to an overhead, horizontal storing position). In such an environment, the purpose of the manual roll-down, spring-loaded roll-up door may be to protect the opened doorway and the warehouse beyond from airborne pests such as insects when the heavy duty door is in the open position, but passage through the doorway is not required. To achieve this desirable function, these doors typically include a curtain in the form of a mesh material, with the mesh being small enough to block most insects, but large enough to allow significant air flow through the door. To further aide in preventing the ingress of insects into the warehouse, such doors typically include guide tracks disposed within vertical members for receiving the side edges of the door, and guiding those side edges in a vertical plane. In addition to performing the guiding function, the guide members may also provide some amount of sealing of the side edges of the curtain to prevent passage of insects.
Similarly, the leading edge of such a door typically also includes a seal to seal between the leading edge of the door and the dock surface below. Of course, one knowledgeable of such installations will appreciate that this lower surface may be the dock floor, or a dock leveler disposed on or in that dock floor. The bottom seal may be some type of deformable material to insure a tight seal between the bottom of the door and the dock floor or leveler. In order for the seal to perform most effectively, the door in its closed position must be accurately vertically positioned. Further, the door should not be subject to any vertical creep by virtue of the spring-loaded roller imparting incidental upward movement to the door.